Re: [PATCH] panic: suppress gnu_printf warning

[Andrew Morton]

On Sun,  7 Jan 2024 17:16:41 +0800 Baoquan He <b...@redhat.com> wrote:

> with GCC 13.2.1 and W=1, there's compiling warning like this:
> 
> kernel/panic.c: In function ‘__warn’:
> kernel/panic.c:676:17: warning: function ‘__warn’ might be a candidate for 
> ‘gnu_printf’ format attribute [-Wsuggest-attribute=format]
>   676 |                 vprintk(args->fmt, args->args);
>       |                 ^~~~~~~
> 
> The normal __printf(x,y) adding can't fix it. So add workaround which
> disables -Wsuggest-attribute=format to mute it.
> 
> ...
>
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -666,8 +666,13 @@ void __warn(const char *file, int line, void *caller, 
> unsigned taint,
>               pr_warn("WARNING: CPU: %d PID: %d at %pS\n",
>                       raw_smp_processor_id(), current->pid, caller);
>  
> +#pragma GCC diagnostic push
> +#ifndef __clang__
> +#pragma GCC diagnostic ignored "-Wsuggest-attribute=format"
> +#endif
>       if (args)
>               vprintk(args->fmt, args->args);
> +#pragma GCC diagnostic pop
>  
>       print_modules();

__warn() clearly isn't such a candidate.  I'm suspecting that gcc's
implementation of this warning is pretty crude.  Is it a new thing in
gcc-13.2?  

A bit of context for gcc@gcc.gnu.org:

struct warn_args {
        const char *fmt;
        va_list args;
};

...

void __warn(const char *file, int line, void *caller, unsigned taint,
            struct pt_regs *regs, struct warn_args *args)
{
        disable_trace_on_warning();

        if (file)
                pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n",
                        raw_smp_processor_id(), current->pid, file, line,
                        caller);
        else
                pr_warn("WARNING: CPU: %d PID: %d at %pS\n",
                        raw_smp_processor_id(), current->pid, caller);

        if (args)
                vprintk(args->fmt, args->args);

        print_modules();

        if (regs)
                show_regs(regs);

        check_panic_on_warn("kernel");

        if (!regs)
                dump_stack();

        print_irqtrace_events(current);

        print_oops_end_marker();
        trace_error_report_end(ERROR_DETECTOR_WARN, (unsigned long)caller);

        /* Just a warning, don't kill lockdep. */
        add_taint(taint, LOCKDEP_STILL_OK);
}